This invention relates generally to a process for recovering a white reaction product of a cyanuric halide with an amine reactant (white being indicative of the product's high purity), in high yield. The first step of the process comprises reacting the cyanuric halide as a finely divided solid with a liquid amine in which the solid is not soluble up to about 50.degree. C. In such a situation, it is conventional to provide a common solvent for the solid and the amine, or at least for one or the other, with the expectation that the solvent will provide the medium in which the reaction may proceed with less restraint than if no solvent was present. Particularly in an industrial environment where a large quantity of product is to be made, it is essential to ensure that the reaction proceeds controllably, and in as little time as is safely practical. These considerations dictate that the choice of an appropriate solvent be the primary consideration in the first step of the process, which was done in the prior art process referred to herein as the "solvent process".
Even if the function of the solvent chosen for the amine was only to disperse the solid cyanuric halide thoroughly in the reaction mass, so that clumping of the solid is avoided, the solvent for the amine discharged a dual function. The solvent maximized the availability of the reactive halogen atoms, and it allowed the reaction to proceed controllably. The substitution of the three halogen atoms on the triazine ring, proceeds in the process of this invention, without a solvent.
More specifically, this invention relates to a process for producing a high purity (at least 97% pure) tri-substituted triazine, the first step of which process comprises substituting each of three chlorine (or other halogen) atoms on a trihalo-s-triazine, specifically cyanuric chloride, with a polysubstituted piperazinone, polysubstituted piperazine, or polysubstituted piperidine ("PSP" for brevity), so as to form a substituted triazine with a PSP substituent at each of the 2, 4 and 6 positions. The substituted triazine is represented by the structure ##STR1## wherein PSP represents a substituent selected from the group consisting of structures ##STR2## wherein, Y represents H or .dbd.O,
R.sub.1 represents C.sub.1 -C.sub.24 alkyl, C.sub.5 -C.sub.7 cycloalkyl, C.sub.7 -C.sub.20 aralkyl, C.sub.1 -C.sub.24 aminoalkyl, and C.sub.6 -C.sub.20 aminocycloalkyl; PA1 R.sub.2, R.sub.3, R.sub.4, and R.sub.5 independently represent C.sub.1 -C.sub.24 alkyl; PA1 R.sub.6, and R.sub.7 independently represent C.sub.1 -C.sub.24 alkyl and polymethylene having from 4 to 7 C atoms which are cyclizable; and, p represents an integer in the range from 2 to about 10; PA1 R.sub.8 represents H, C.sub.1 -C.sub.6 alkyl and phenyl; and, ##STR3## wherein Me=methyl, R.sup.6 represents hydrogen, oxyl oxygen, C.sub.1 -C.sub.12 -alkyl, C.sub.3 -C.sub.7 -alkenyl, C.sub.7 -C.sub.11 -phenylalkyl, cyanomethyl, C.sub.2 -C.sub.18 -alkanoyl, or C.sub.3 -C.sub.18 -alkenoyl, or a group --CON(R.sup.7)(R.sup.8) in which R.sup.7 is C.sub.1 -C.sub.12 -alkyl, allyl, cyclohexyl, benzyl, phenyl, or C.sub.7 -C.sub.12 -alkylphenyl, and R.sup.8 is hydrogen, C.sub.1 -C.sub.12 -alkyl, allyl or benzyl or R.sup.7 or R.sup.8 together with the N atom to which they are attached, form a 5-membered ring or 6-membered heterocyclic ring; and, PA1 X is a divalent group of the formula --O--, --NH--CH.sub.2 --CH.sub.2 --, --NH--(CH.sub.2).sub.2 --O-- and the like.
Such triazines substituted with a polysubstituted piperazinone are referred to in U.S. Pat. Nos. 4,480,092 and 4,692,752 as "PIP-Ts" (acronym for piperazinone-triazine) which are disclosed as being stabilizers for organic compounds. Other triazines tri-substituted with a polysubstituted piperidine are referred to in U.S. Pat. No. 4,731,393, the disclosure of which is incorporated by reference thereto as if fully set forth herein. All tri-substituted triazines are referred to herein as PIP-Ts irrespective of the PSP substituents.
The PIP-T tri-substituted with polysubstituted piperazinones, and precursor mono- and di-substituted PIP-Ts, were prepared by dispersing finely divided solid cyanuric halide such as cyanuric chloride in an aromatic solvent such as toluene, or an aliphatic solvent such as hexane, and reacting the cyanuric chloride with the PSP amine reactant (hereafter "amine reactant" for brevity) from which the PSP substitutent is to be derived. Typically, the amine reactant was dissolved in toluene or an aliphatic solvent such as hexane, and the reaction carried out at elevated temperature with the addition of dilute aqueous alkali. NH.sub.4 OH or an alkali metal hydroxide, say NaOH, are used to neutralize the hydrogen halide, such as HCl generated during the reaction of cyanuric chloride with the amine reactant. The alkali was used to neutralize the HCl generated during the reaction, before the HCl could react with the amine reactant present. The prior art reaction was not carried out under essentially anhydrous conditions.
This laboratory process was subsequently scaled up for commercial production of PIP-Ts, except that, to obtain a commercially acceptable yield of product in a reasonable period of time, say 14 hr, it became necessary to use a larger excess of amine reactant, still requiring a large amount of solvent; and, it became necessary to carry out the reaction at a temperature in excess of 175.degree. C. at a pressure in excess of 150 psig. Under carefully controlled conditions, the yield of acceptable PIP-T product was typically no more than 80%; the quality of the desired PIP-T product was vitiated; undesirable by-products were formed; and, the excess amine reactant was not economically recoverable. The recovery of at least 80%, and preferably more than 90%, of the excess amine reactant used in the first step of the process, is critical to the commercial success of the process because, typically, the cost of the amine reactant is many times greater than that of cyanuric halide, all of which cyanuric halide must be converted to the tri-substituted triazine product if it is to be substantially the only cyanuric halide/amine reactant reaction product to be recovered.
The tri-substitution of the halogens on a cyanuric halide with polysubstituted piperidines was conventionally done in toluene as solvent, and at low temperature, with the result that the reaction is too slow to be commercially feasible.
The process of this invention provides a solventless reaction mass in which the desired reaction (the first step of this process) proceeds at relatively high speed, at practical low temperature and pressure under essentially anhydrous conditions. In a subsequent step, the deliberate addition of an appropriate preselected amount of a lower C.sub.1 -C.sub.6 branched or straight chain alkanol, first to thin the thick solution which typically results after the reaction is complete, and then the addition of aqueous alkali to form the salt, was found unexpectedly to precipitate salt, usually NH.sub.4 Cl or NaCl, from solution in a mixture of three liquids, namely: unreacted excess (XS) amine reactant, alkanol and a relatively very small amount of water, in which mixture the PIP-T product is dissolved. In still another subsequent step, the deliberate addition of more water to the NaCl-free mixture of alkanol, and XS amine reactant produced more product, as it was discovered that this procedure precipitated the desired PIP-T product in essentially pure form.
The key to the effectiveness of the process is the forced solubility of solid cyanuric halide in the amine reactant with immediate subsequent displacement of a first halogen atom. Displacement of the first halide atom might be expected to occur relatively easily, that is, at relatively low temperature, and it does.
But the second halogen atom is not as easily displaced as was the first, and it is even more difficult to displace also the third. In the absence of a solvent, at the elevated temperature one would expect to use to trisubstitute the triazine ring, it was not evident that the halogen atoms would be displaced by only the H atom on the terminal N atom of the PSP, to the exclusion of the H atom on the N.sup.4 atom of the piperazinone ring. Still further, since it was evident that, irrespective of which H atom displaced the Cl, Br, or F atoms on the triazine ring, the HCl, HBr or HF formed would react with the amine reactant making it unavailable for reaction with the cyanuric halide, carrying out the reaction in the absence of an alkali, seemed ingenuous.
Moreover, because there was no readily adaptable process to recover the XS amine reactant from the hydrochloride (say) of the XS amine reactant, not to mention removing the salt formed, the solventless reaction of the first step seemed misdirected. Recovering and recycling the XS amine reactant is an essential factor of the process because of the high cost of the amine reactant. Yet, because this solventless reaction proceeds relatively rapidly (less than 12 hr) with more than 80% yield of product under less than 5 atm pressure, and preferably at substantially atmospheric pressure, it spurred the exploration of techniques to overcome the problems generated by the first step. It is this exploration which opened the door to the solutions embodied in the several subsequent steps which together provide a highly effective process for making the product.